1. Field of the Invention
The present invention relates to an apparatus and method for entering characters in a portable terminal. More particularly, the present invention relates to a character entry apparatus and method for reducing the number of key presses and the number of wrong entries in a portable terminal.
2. Description of the Related Art
Typically, a small-size portable terminal has a limited number of keys, for example, 10 to 12 keys to enter characters with. For languages having 10 to 12 characters in their alphabet, one character is allocated to each key. However, for languages that have a greater number of characters in their alphabet, one key-to-one character assignment is not possible.
FIG. 1 is a diagram illustrating a keypad in a portable terminal, configured to enter Japanese characters according to a Japanese standard.
Referring to FIG. 1, the Japanese characters of the Japanese alphabet (Hiragana) are arranged in order by groups of five characters for assignment to each key. For example, a group of  is allocated to a digit “1” key, and a group of  to a digit “2” key. In this manner, a plurality of characters may be allocated to the other digit keys and each digit key is imprinted with the first character of a corresponding group.
On a keypad with the above Japanese alphabet layout, a user enters text in a multi-tap fashion. For example, to enter a word  he presses the digit “2” key twice for entering  presses the digit “1” key four times for entering  and presses the digit “9” key five times for entering  The word  takes a total of 10 taps.
For most languages, character entry relies on the multi-tap scheme. Because of mapping between a plurality of characters and one key, the multi-tap scheme is not user-friendly and is vulnerable to an incorrect entry. To solve this problem, a single-tap character entry scheme was proposed. For details about the single-tap scheme, see T9 (http//www.T9.com), eZi (http//gcorp.com), itap (http//www.mot.com/lexicus/html/itap.html), and for the Japanese language, POS (http//www.muchy.com), the entire disclosures of all of which are hereby incorporated by reference. In the single-tap scheme, one tap or key press is sufficient for entry of one character. This entry scheme is based on an algorithm which automatically displays a word matching to a combination of input characters after searching a dictionary of a given language.
By way of example for the English language, to enter “boy” by the single-tap scheme, the user presses the digit “1” key having the letters “ABC” imprinted thereon for entering “b”, the digit “6” key for entering “o”, and the digit “9” key for entering “y”. Upon entry of the first character “b”, a given dictionary is searched with “b” used as a search key, and upon entry of the second character “o”, “bo” is used as a search key. Finally, upon entry of the last character “y”, the dictionary is searched using “boy” as a search key. Since “boy” is registered in the dictionary, the user selects “boy”.
3×3×3 character combinations can be created using three keys ABC, MNO and WXY. With the first key press, “ABC” is entered at once, and with the second key press “MNO” is entered at once, thereby displaying the possible combinations of letters in ABC times MNO, such as AM, AN, AO, BM, BN, BO, CM, CN, CO. Here, the desired character combination is “bo”. The system continuously searches the dictionary for the next character entry despite the possibility of there being correct words among the two-character combinations, and finally identifies the desired word. During the process, the character combinations associated with the key presses, which can be used as the beginning of the desired word, for example, “bo”, can be selected and displayed continuously. Then, the dictionary is searched in order to find all of the words, which include “bo” in the beginning of the words, and displays the resulting words. The user can identify and select the desired word among the words that the system speculates and displays.
As described above, the single-tap scheme has recently emerged as a character entry technique for a small-size keypad with a limited number of keys, thereby substituting for the multi-tap scheme. The single-tap scheme pursues the efficiency of character entry through a reduction of the number of key presses- and increases the likelihood of accurate character entry.
As previously stated, a plurality of characters are inevitably allocated to a single key in a keypad with a limited number of keys and thus one character is accessed by the multi-tap scheme, despite the shortcomings of a large number of key presses and frequent wrong entry.
On the other hand, while the single-tap scheme is effective in reducing the number of key presses, it requires a dictionary for a given language and updating of the dictionary with newly coined words, new abbreviations, or the like. In practice, it is not possible to include every needed word in a rapidly developing information and communication environment, such as person names, Internet addresses, home addresses, or the like. What is worse, for a word not registered in the dictionary, the single-tap scheme must be used in conjunction with the multi-tap scheme. In this context, the one-key-for-one-letter method has its own limitations and increases system load due to a large number of character combinations resulting from a plurality of character entries and the accompanying directional searches.
Accordingly, there is a need for an improved apparatus and method for character entry to substantially solve problems encountered with the multi-tap and single-tap schemes.